1. Field of the Invention
The present invention relates to a fluid seal and, more particularly, to a shaft seal which may be suitably used in automotive shock absorbers and the like for sealing a reciprocating shaft which undergoes a substantial lateral thrust.
2. Description of the Prior Art
In an automotive shock absorber, the piston rod is sealed by a shaft seal with respect to the housing. The shaft seal includes a primary fluid sealing lip for sealing the oil side of the piston rod to prevent release of the hydraulic fluid contained in the housing. In most instances, the seal also includes a dust sealing lip for sealing the air side to protect the primary sealing lip from ingress of dust and dirt.
During operation of the shock absorber, the piston rod undergoes a substantial lateral thrust as the wheel hits a bump or when the automobile undergoes cornering. In particular, a severe lateral thrust is encountered in the MacPherson strut type suspension systems.
One of the problems which must be overcome in designing a shaft seal for shock absorber applications is to effectively prevent ingress of dust and dirt for a long period of time despite repeated lateral thrust.
Japanese Utility Model Kokai Publication No. 6-28429 discloses a shaft seal which is provided with an auxiliary dust sealing lip situated inwardly of the primary dust sealing lip. The auxiliary dust sealing lip is profiled in the form of an edge that functions to scrape incoming dust and dirt back to the air side.
The problem associated with the conventional shaft seal is that the auxiliary dust sealing lip undergoes a considerable wear so that the dust sealing function of the shaft seal is prematurely degraded.
It is therefore an object of the present invention to provide a shaft seal which is capable of providing a high degree of dust sealing capability for a long period of time.